This invention relates generally to improved catalysts for a variety of chemical processes. In particular, this invention relates to catalysts supported on polyoxometallate salts.
In general, catalysts are well known for a variety of chemical processes. For example, certain oxidation catalysts are particularly useful for the preparation of products, such as alcohols, carboxylic acids, alkenes, alkynes, and the like, from alkanes. One class of catalysts, heteropolyacids, are known to be supported, e.g., on polyoxometallate salts, to improve their performance and because of their inherent instability. For example, US 5,705,685 (Lyons et al.) discloses heteropolyacids supported on polyoxometallate salts for the oxidation of alkanes to unsaturated carboxylic acids. No other catalysts are disclosed in Lyons et al.
Although many catalysts, such as mixed metal oxides are often supported, others, such as vanadium phosphorus compounds, are typically not supported because these catalysts perform poorly when supported and are stable by themselves. However, since reaction takes place on the surface of most heterogeneous catalysts, there has been a growing interest in supporting catalysts in order to maximize the catalyst surface, and thus improve performance. Such supports include silica, zirconia, alumina, titania, diatomaceous earth, and the like. However, such supports often produce catalysts with low selectivities.
Herron et al., Molecular Precursors to Vanadyl Pyrophosphate and Vanadyl Phosphite, Journal of the American Chemical Society, vol. 119, 7149-7150 (1997), disclose the need for supported vanadium phosphorus catalysts, particularly for the production of maleic anhydride. Traditional methods of catalyst preparation have made it difficult to prepare the desired high surface area supported catalysts having well defined stoichiometry and phase. Herron et al disclose specific molecular clusters of vanadyl catalysts as a method of supporting such catalysts on silica. However, such molecular clusters are not easily adaptable to supporting other types of catalysts. Herron et al. do not disclose supporting such molecular clusters on any other supports.
Thus, there is a continuing need for supported catalysts having a maximized surface area, a controlled surface area and high selectivities.
It has been surprisingly found that polyoxometallate salts can be used to support a variety of catalysts.
In one aspect, the present invention is directed to a catalyst composition including a catalyst situated on a polyoxometallate support; wherein the polyoxometallate support has the formula
QaH(exe2x88x92az)(XkMmxe2x88x92xM1xM2nOy)xe2x88x92exe2x80x83xe2x80x83(I)
wherein Q, is a cation selected from potassium, rubidium, cesium, magnesium, calcium, strontium, barium, transition metal, actinide metal, lanthanide metal, metal oxy ion, ammonium, tetraalkylammonium, pyridinium, quinolinium, protonated aromatic amines, protonated aliphatic amines or mixtures thereof; X is an element selected from Groups 3-16 elements; M=molybdenum, tungsten or a combination thereof, M1=vanadium; M2 is a transition metal different from M and M1; z=the charge on Q; k=1 to 5; m=5 to 20; n=0 to 3; x=0 to 6; y=18 to 62; and e is the charge of the polyoxometallate anion; and
provided that the catalyst is not a heteropolyacid.
In a second aspect, the present invention is also directed to a process for preparing a catalyst composition including a catalyst situated on a polyoxometallate support; wherein the polyoxometallate support has the formula
QaH(exe2x88x92az)(XkMmxe2x88x92xM1xM2nOy)xe2x88x92exe2x80x83xe2x80x83(1)
wherein Q is a cation selected from potassium, rubidium, cesium, magnesium, calcium, strontium, barium, transition metal, actinide metal, lanthanide metal, metal oxy ion, ammonium, tetraalkylammonium, pyridinium, quinolinium, protonated aromatic amines, protonated aliphatic amines or mixtures thereof; X is an element selected from Groups 3-16; M is as defined above; M1=vanadium; M2 is a transition metal different from M and M1; z=the charge on Q; k=1 to 5; m=5 to 20; n=0 to 3; x=0 to 6; y=18 to 62; and e is the charge of the polyoxometallate anion; including the step of admixing the catalyst with the polyoxometallate support; provided that the catalyst is not a heteropolyacid.
In a third aspect, the present invention is directed to a process for preparing unsaturated organic compounds including the steps of contacting an alkane with an oxidizing agent and a catalyst composition including one or more mixed metal oxides, vanadium phosphorus compounds or mixtures thereof situated on a polyoxometallate support; wherein the mixed metal oxide has the formula
Aaxe2x80x2M3mxe2x80x2LlZzxe2x80x2Ooxe2x80x83xe2x80x83(II)
wherein A is selected from molybdenum, tungsten, iron, niobium, tantalum, zirconium, ruthenium, and mixtures thereof; M3 is selected from vanadium, cerium, chromium, and mixtures thereof; L is selected from tellurium, bismuth, antimony, selenium, and mixtures thereof; Z is selected from niobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium, manganese, iron, ruthenium, cobalt, rhenium, nickel, palladium, platinum, antimony, bismuth, boron, indium, cerium, and mixtures thereof; axe2x80x2=0.25 to 0.98; mxe2x80x2=0.003 to 0.5; l=0.003 to 0.5; zxe2x80x2=0.003 to 0.5; o is dependent on the oxidation state of the other elements; and
wherein the polyoxometallate support has the formula
QaH(exe2x88x92az)(XkMmxe2x88x92xM1xM2nOy)xe2x88x92exe2x80x83xe2x80x83(II)
wherein Q is a cation selected from potassium, rubidium, cesium, magnesium, calcium, strontium, barium, transition metal, actinide metal, lanthanide metal, metal oxy ion, ammonium, tetraalkylammonium,pyridinium, quinolinium, protonated aromatic amines, protonated aliphatic amines or mixtures thereof; X is an element selected from Groups 3-16 elements; M=molybdenum, tungsten or a combination thereof; M1=vanadium; M2 is a transition metal different from M and M1; z= the charge on Q; k=1 to 5; m=5 to 20; n=0 to 3; x=0 to 6; y=18 to 62; and e is the charge of the polyoxometallate anion.
In a fourth aspect, the present invention is directed to a process for preparing a mixed metal oxide catalyst of the formula
Aaxe2x80x2M3mxe2x80x2LlZzxe2x80x2Ooxe2x80x83xe2x80x83(II)
wherein A is selected from molybdenum, tungsten, iron, niobium, tantalum, zirconium, ruthenium, and mixtures thereof; M3 is selected from vanadium, cerium, chromium, and mixtures thereof; L is selected from tellurium, bismuth, antimony, selenium, and mixtures thereof; Z is selected from niobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium, manganese, iron, ruthenium, cobalt, rhenium, nickel, palladium, platinum, antimony, bismuth, boron, indium, cerium, and mixtures thereof; axe2x80x2=0.25 to 0.98; mxe2x80x2=0.003 to 0.5; l=0.003 to 0.5; zxe2x80x2=0.003 to 0.5; o is dependent on the oxidation state of the other elements; including the step of heating a mixed metal oxide molecular precursor at a temperature of at least 600xc2x0 C. for a period of time sufficient to convert the precursor to the mixed metal oxide.